Glycoconjugated Polymer. 5. Synthesis and Characterization of a Seven-Arm Star Polystyrene with a β-Cyclodextrin Core Based on TEMPO-Mediated Living Radical Polymerization

Abstract

β-Cyclodextrin (β-CyD) was modified into a seven-functional initiator (1) for 2,2,6,6-tetramethylpiperidinyloxy- (TEMPO-) mediated living radical polymerization. Styrene (St) was polymerized with 1 under several conditions to afford original products I−IV. Size exclusion chromatography (SEC) traces of I−IV exhibited trimodal molecular weight distributions; hence, they were fractionated into the respective three species, i.e., main products 2, byproducts 3 with lower molecular weights, and byproducts 4 with higher molecular weights. The weight-average molecular weights determined by SEC and static laser light scattering measurement (Mw,SEC and Mw,SLS, respectively) were 1.34 × 104 and 2.98 × 104 for 2-I, 4.52 × 104 and 6.77 × 104 for 2-II, 1.35 × 105 and 1.87 × 105 for 2-III, and 9.67 × 105 and 1.89 × 106 for 2-IV. The Mw,SLS's were larger than the respective Mw,SEC's. In the 1H NMR spectra of 2, the signals due to polystyrene (PSt) appeared along with the characteristic signals due to the 1 unit. Therefore, those of 2 were assignable to a star PSt with an acetylated β-CyD core. Polymer 2 was treated with sulfuric acid to give core-cleaved polymer 2‘. The Mw,SEC's were 2.80 × 103, 9.60 × 103, 2.70 × 104, and 2.61 × 105 for 2‘-I, 2‘-II, 2‘-III, and 2‘-IV, indicating that the arm number of 2, NPSt, was seven. The byproducts 3 and 4 were characterized and found to be a TEMPO-terminated linear PSt and a star−star coupled polymer, respectively. The seven-arm star PSt with a β-CyD core, 5, was obtained through deacetylation of 2 using sodium methoxide in dry THF. The Mw,SLS values were 3.96 × 105, 3.78 × 105, 2.40 × 105, and 1.94 × 106 for 5-I, 5-II, 5-III, and 5-IV. Hence, 5-I and 5-II showed aggregation in a good solvent for PSt with aggregation-numbers (NA) of 13 and 6, respectively.